For observation of a microscopic region of an object, scanning electron microscopes (SEMs) and transmission electron microscopes (TEMs) and the like are used. Generally, in these apparatuses, a second casing in which to dispose a sample is evacuated to establish a vacuum state as an atmosphere for the sample, before imaging. On the other hand, there has been a great need to observe samples such as biochemical samples and liquid samples with the use of both an optical microscope and an electron microscope in an atmospheric pressure, and not in a vacuum where those samples will be deteriorated or state-changed. In recent years, SEM apparatuses have been developed to observe an objective sample under an atmospheric pressure.
These apparatuses, in principle, have a configuration wherein a diaphragm permitting transmission of an electron beam therethrough is provided between an electrooptic system and a sample to partition part of a vacuum state and part of an atmospheric air state from each other. Thus, all these apparatuses have a common feature that a thin film is provided between a sample and an electrooptic system.
Patent Document 1 describes an atmospheric-pressure SEM having a configuration wherein an electron optical column is disposed with its electron source side directed downward and with its objective lens side directed upward, and a thin film transmissive to an electron beam is provided on the side of an electron beam emission hole at the terminal end of the electron optical column. In the invention described in Patent Document 1, the objective sample to be observed is mounted directly on the thin film, the sample is irradiated with a primary electron beam from below, and reflected electrons or secondary electrons are detected, thereby performing SEM observation. The sample is disposed inside an annular member (which is placed in the periphery of the thin film) but in a thin film-formed liquid. Thus, the document describes an atmospheric-pressure SEM suitable for use to observe a sample in a liquid, particularly. In addition, it is described that the optical microscope and the electron microscope are so disposed that their optical axes are coaxial, whereby both optical microscope observation and electron microscope observation can be performed.
In addition, Patent Document 2 describes an apparatus configuration wherein an optical microscope and an electron microscope equipped with a diaphragm are aligned, whereby a sample placed under an atmospheric pressure is observed alternately by the optical microscope and an electron microscope.